1. Field of the Invention
This invention relates to a process for catalytically cracking hydrocarbons to lower boiling hydrocarbon products. It relates particularly to a catalytic cracking process for the production of a maximum amount of hydrocarbon components boiling in the middle distillate range, which are useful, for example, as heating oil.
2. Description of the Prior Art
It is known to optimize the production of gasoline fractions by recycling pyrolitic olefin-containing naphtha to a catalytic cracking zone. Such processes are disclosed, for example, in U.S. Pat. Nos. 3,692,667 and 3,706,654 which teach that a recycle naphtha is subjected to conversion prior to adding the resulting cracked product to the principal conventional catalytic cracking hydrocarbon charge to be cracked.
U.S. Pat. No. 3,758,400 teaches that the addition of small amounts of a debutanized aromatic concentrate containing olefinic and diolefinic hydrocarbons to a conventional catalytic cracking feedstock containing a recycle gas oil results in the formation of increased yield of gasoline of improved octane number when processed over a cracking catalyst.
U.S. Pat. No. 2,608,524 teaches that a superior motor fuel can be produced by cracking a mixture of a straight run naphthenic naphtha and a gas oil in the presence of a bauxite catalyst.
It is also known that hydrocarbons can be catalytically cracked in the presence of added normally gaseous olefins to yield an effluent rich in unsaturated hydrocarbons of the motor fuel boiling range, as disclosed in U.S. Pat. No. 2,626,233.
U.S. Pat. No. 2,464,810 teaches that heavy crude oils or tar can be catalytically cracked to produce a motor fuel by dissolving the heavy oil or tar in a naphtha solvent and subsequently subjecting the solution to a cracking reaction. Part of the naphtha fraction recovered from the catalytic cracking reaction product can be used as naphtha solvent for the heavy feed.
It has now been found unexpectedly that an increased yield and selectivity to middle distillate boiling range components can be produced by catalytically cracking a conventional catalytic cracking hydrocarbon feedstock, such as a gas oil, in the presence of an additional normally liquid olefin-containing naphtha. The term "naphtha" is used herein to refer to a mixture of hydrocarbons boiling (at atmospheric pressure) in the range of about C.sub.5 to 430.degree.F. The term "normally liquid olefins" is used herein to refer to olefins boiling (at atmospheric pressure) in the same range as that of the naphtha.